The present invention relates generally to a system and method for controlling the ignition characteristics of certain internal combustion engines, and particularly to a system and method for utilizing feedback from a combustion condition sensor to adjust the air-fuel mixture to a more optimal ratio.
Internal combustion engines are used in a wide variety of applications, including providing power for a variety of vehicles. Generally, such engines include one or more cylinders that each contain a piston designed for movement in a reciprocating manner. Each piston is connected to a crankshaft by a connecting rod that delivers force from the piston to the crankshaft in a manner that rotates the crankshaft. Power to drive the piston is provided by igniting an air-fuel mixture supplied to the cylinder on a side of the piston opposite the connecting rod. The air-fuel mixture is ignited by some type of ignition device, e.g. providing a spark across electrodes of a spark plug.
Air and fuel may be supplied to each cylinder by a variety of mechanisms, e.g. a fuel injection system. Regardless of how the air-fuel mixture is established, it is necessary to adjust or change the air-fuel mixture according to operating conditions. For example, application of greater throttle for increased engine speed requires a greater quantity of fuel. On the other hand, maintaining the engine operation at a lower rpm, requires a lesser quantity of fuel supplied to each cylinder. Generally, greater control over combustion conditions, e.g. air-fuel mixture, provides an engine designer with a greater ability to bring about a desired engine performance under a greater range of operating conditions.
Modern engines often utilize electronic fuel injection systems that inject specific amounts of fuel based on a stored fuel map. The fuel map effectively acts as a guide to fuel injection quantities based on a variety of sensed parameters, such as engine speed, throttle position, exhaust pressure and engine temperature. However, none of these inputs are based on the actual combustion taking place in the one or more cylinders.
In some applications, oxygen sensors have been used to sense oxygen content of the combustion products, i.e. exhaust gasses. This information can be used to determine data about the constituents ignited or combusted in the cylinder. However, such closed-loop feedback has not been fully utilized in optimizing the air-fuel ratio to obtain desired combustion characteristics over a broad range of operating conditions.
The present invention features a method for controlling an internal combustion engine having a plurality of cylinders. Each cylinder is capable of operating in a stratified combustion mode and a homogeneous combustion mode. The method includes sequentially changing a plurality of cylinders in an engine from a stratified combustion mode to a homogeneous combustion mode. The method further includes sensing a combustion condition in at least one cylinder of the plurality of cylinders. The sensing typically is accomplished during the homogeneous combustion mode of the at least one cylinder. The method further includes adjusting the air-fuel ratio in the at least one cylinder based on the combustion condition.
According to another aspect of the present invention, a method is provided for promoting more optimal performance from a watercraft powered by an internal combustion engine. The method includes powering the watercraft with an engine having a plurality of cylinders that are sequentially changed from stratified combustion mode to homogeneous combustion mode. Again, the combustion condition in at least one cylinder is sensed during homogeneous operation. Also, the air-fuel ratio in at least one cylinder based on the combustion condition.
According to another aspect of the invention, a system is provided for optimizing combustion parameters in an engine. The system includes an internal combustion engine having a plurality of cylinders into which fuel is directly injected. The system also includes a sensor disposed in fluidic communication with a cylinder of the plurality of cylinders. The sensor is designed to sense a particular combustion condition. Also, an electronic controller is utilized for delivery of fuel to each cylinder. The controller includes a plurality of mapped values for fuel quantities to be injected. When the electronic controller receives an input from the sensor, it corrects the plurality of mapped values according to the input. This permits the air-fuel ratio to be optimized relative to the previously mapped values for a given set of operating conditions.